1. Field of the Invention
The present invention relates to a connecting structure between an electrode and a lead, an electric double layer capacitor having the structure, and a method for manufacturing the capacitor, and more particularly to a connecting structure between an electrode and a lead, which may keep a capacitance of a capacitor and improve contact reliability, an electric double layer capacitor having the structure, and a method for manufacturing the capacitor.
2. Description of the Related Art
An ultra capacitor has a capacitance at least 300 times of that of a conventional capacitor. In addition, the ultra capacitor may store a relatively smaller amount of energy than a battery, but it may supply an instantaneous peak power within a very short time about 10 to 100 times of a battery. Thus, the ultra capacitor is used as an energy device that substitutes or supplements a battery.
An electric double layer capacitor, one of ultra capacitors, stores charges in an ionic layer, so-called an electric double layer, formed in an interface of electrolyte by using the electricity storing mechanism, different from a battery that uses chemical reactions. That is to say, the ultra capacitor stores electricity in a way of physical charge accumulation. Thus, the ultra capacitor does not exhibit any deterioration caused by repeated uses and has no limitation in its life cycle. Considering the above features, the ultra capacitor is used as an energy device that requires a long time use without needing a large amount of energy.
In a general electric double layer capacitor, positive and negative electrode foils and corresponding lead wires are joined by means of supersonic welding, caulking or compressing.
Junctions made by supersonic welding are advantageous in low resistance since metals are coupled with each other. However, the supersonic welding junctions are not advantageous in that a sufficient junction force is not ensured due to the effects of a dielectric oxide layer formed on a surface of the positive electrode foil. In addition, there is another problem that impurities caused by sparks generated during the supersonic welding process are adhered to the supersonic welding junctions.
Junctions made by caulking are advantageous since they may give a sufficient junction force. However, there is a problem that a relatively high contact resistance is caused between the positive and negative electrode foils and the lead wires.
Junctions made by compression show a low contact resistance since metals may be closely coupled with each other, similarly to the supersonic welding. However, there is a problem that they give a lower junction force than the supersonic welding junctions and the caulking junctions.